Refrigeration device

ABSTRACT

A refrigeration device includes: a refrigerator; a heat pipe that includes a condensation unit connected to the refrigerator and adapted to condense a refrigerant, includes an evaporation unit connected to a storage chamber and adapted to evaporate the refrigerant, and includes a piping for circulating the refrigerant between the condensation unit and the evaporation unit; a heat pipe temperature sensor that detects a temperature of the heat pipe; and a control unit that controls driving of the refrigerator based on a result of detection by the heat pipe temperature sensor. The control unit controls the refrigerator so that the temperature of the heat pipe does not fall below a standard boiling temperature of the refrigerant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of InternationalPatent Application No. PCT/JP2018/019116, filed on May 17, 2018, whichclaims the benefit of priority of Japanese Patent Application No.2017-132136, filed on Jul. 5, 2017, the entire content of each of whichis incorporated herein by reference.

BACKGROUND Field of the Invention

The present invention relates to refrigeration devices, and, moreparticularly, to a refrigeration device adapted to condense arefrigerant and then exhibit a cooling action by evaporating therefrigerant.

Description of the Related Art

Refrigeration devices configured to exchange heat between a refrigeratorand a low-temperature storage chamber via a heat pipe connected to thecooling unit of the refrigerator are known (see, for example, patentliterature 1). In the refrigeration device disclosed in patentliterature 1, a gas entrapment for adjusting the pressure inside theheat pipe is provided.

-   [Patent literature 1] JP8-320165

A heat pipe is a structure to transfer heat by using liquification of anentrapped refrigerant. Therefore, the internal pressure of the heat pipeis increased significantly while the heat is not being transferred,i.e., while the refrigeration device is being stopped than while theheat is being transferred, i.e., while the refrigeration device is beingin operation. If ambient air enters the heat pipe during the operationof the refrigeration device, therefore, the internal pressure of theheat pipe will be excessive when the refrigeration device is stopped,with the result that the heat pipe might be damaged or broken. In arefrigeration device provided with a heat pipe, therefore, it is desiredto inhibit entry of ambient air into the heat pipe. We have studiedrefrigeration devices provided with a heat pipe extensively and haverecognized that there is room for improvement in related-artrefrigeration devices in regard to inhibition of entry of ambient airinto the heat pipe.

SUMMARY OF THE INVENTION

The present disclosure addresses the above-described issue, and anillustrative purpose thereof is to provide a technology for inhibitingentry of ambient air into a heat pipe.

An embodiment of the present embodiment relates to a refrigerationdevice. The refrigeration device includes: a refrigerator; a heat pipethat includes a condensation unit connected to the refrigerator in amanner that heat exchange is enabled and adapted to condense arefrigerant, includes an evaporation unit connected to a storage chamberfor housing an object that should be stored in a manner that heatexchange is enabled and adapted to evaporate the refrigerant, andincludes a piping for circulating the refrigerant between thecondensation unit and the evaporation unit; a heat pipe temperaturesensor that detects a temperature of the heat pipe; and a control unitthat controls driving of the refrigerator based on a result of detectionby the heat pipe temperature sensor. The control unit controls therefrigerator so that the temperature of the heat pipe does not fallbelow a standard boiling temperature of the refrigerant.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a perspective view showing a schematic structure of alow-temperature storage in which the refrigeration device according toembodiment 1 is installed;

FIG. 2 is a rear view showing a schematic structure of thelow-temperature storage;

FIG. 3 is an enlarged view of area A bounded by the broken line in FIG.2;

FIG. 4 is a flowchart showing an example of control performed in therefrigeration device according to the embodiment 1;

FIG. 5 is a flowchart showing an example of control performed by therefrigeration device according to embodiment 2;

FIGS. 6A and 6B are charts showing an example of transition of theinside temperature and the piping temperature;

FIG. 7A is a perspective view showing a schematic structure of alow-temperature storage in in which the refrigeration device accordingto embodiment 3 is installed;

FIG. 7B is a plan view showing a schematic structure of thelow-temperature storage; and

FIG. 8 is a flowchart showing an example of control performed by therefrigeration device according to embodiment 3.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferredembodiments. This does not intend to limit the scope of the presentinvention, but to exemplify the invention.

Hereinafter, the invention will be described based on preferredembodiments with reference to the accompanying drawings. The preferredembodiments do not intend to limit the scope of the invention butexemplify the invention. Not all of the features and the combinationsthereof described in the embodiments are necessarily essential to theinvention. Identical or like constituting elements, members, processesshown in the drawings are represented by identical symbols and aduplicate description will be omitted. The scales and shapes of therespective parts shown in the figures are defined for convenience's saketo make the explanation easy and shall not be interpreted limitativelyunless otherwise specified. Terms like “first”, “second”, etc. used inthe specification and claims do not indicate a sequence or degree orimportance by any means unless otherwise specified and are used todistinguish a certain feature from the others.

Embodiment 1

FIG. 1 is a perspective view showing a schematic structure of alow-temperature storage in which the refrigeration device according toembodiment 1 is installed. FIG. 2 is a rear view showing a schematicstructure of the low-temperature storage. FIG. 3 is an enlarged view ofarea A bounded by the broken line in FIG. 2. FIG. 2 is a transparentview of the interior of the low-temperature storage. A low-temperaturestorage 1 (1A) is used to store a biological material such as a cell anda tissue of a living body, a medication, a reagent, etc. at a lowtemperature. The low-temperature storage 1 includes a heat insulationbox body 2 with an open top and a machine room 4 provided adjacent tothe heat insulation box body 2.

The heat insulation box body 2 includes an outer box 2 a with an opentop and an inner box 2 b with an open top. The space between the outerbox 2 a and the inner box 2 b is filled with a heat insulator (notshown). The heat insulator is made from, for example, a polyurethaneresin, a glass wool, and a vacuum heat insulator. The space in the innerbox 2 b defines a storage chamber 6. The storage chamber 6 is a space inwhich an object that should be stored is housed. The targetedtemperature inside the storage chamber 6 (hereinafter, referred to asinside temperature as appropriate) is, for example, −50° C. or below. Aninside temperature sensor 44 is provided at a predetermined position inthe storage chamber 6. The inside temperature sensor 44 senses theinside temperature, generates a detection value based on the sensedtemperature, and outputs the detection value to a control unit 36described later.

A heat insulation door 8 is provided on the top surface of the heatinsulation box body 2 via a packing. A heat insulation door 8 is fixedat one end to the heat insulation box body 2 and is provided to berotatable around the one end. This heat insulation door 8 ensures thatthe opening of the storage chamber 6 can be opened or closed as desired.The other end of the heat insulation door 8 is provided with a handle 10maneuvered to open or close the heat insulation door 8. An evaporationunit 26 of a heat pipe 16 described later is provided on the wallsurface of the inner box 2 b toward the heat insulator. The interior ofthe storage chamber 6 is cooled due to evaporation of the refrigerant inthe evaporation unit 26.

The machine room 4 is a space that houses a refrigeration device 12according to the embodiment except that a part of a piping 28 of theheat pipe 16 and the evaporation unit 26 are provided in the heatinsulation box body 2. The machine room 4 is spaced apart from thestorage chamber 6. A cooling unit 22 of the refrigerator 14, acondensation unit 24 of the heat pipe 16, and a part of a piping 28,which are provided in the machine room 4, are covered by a heatinsulator (not shown) and are thermally insulated from the environment.The heat insulator is made from, for example, a urethane resin, a glasswool, and a heat insulating rubber. The structure of the heat insulationbox body 2 and the machine room 4 is publicly known so that adescription of further details is omitted.

The refrigeration device 12 is a device capable of cooling the interiorof the storage chamber 6 to an extremely low temperature of −50° C. orbelow. The refrigeration device 12 includes a refrigerator 14, the heatpipe 16, a refrigerant chamber 18, a heat pipe temperature sensor 42,and a control unit 36.

The refrigerator 14 is a device for cooling the condensation unit of theheat pipe 16. The refrigerator 14 is provided in the machine room 4. Apublicly known refrigerator such as a Gifford-McMahon (GM) refrigerator,a pulse tube refrigerator, a Stirling refrigerator, a Solvayrefrigerator, a Claude cycle refrigerator, and a Joule Thomsonrefrigerator can be used as the refrigerator 14. The refrigerator 14includes a cooling unit 22 adapted to absorb the external heat. Thestructure of the refrigerator 14 is publicly known so that a descriptionof further details is omitted.

The heat pipe 16 is a device for cooling a target of cooling by usingthe vaporization heat of the refrigerant and mediates heat exchangebetween the cooling unit 22 of the refrigerator 14 and the interior ofthe storage chamber 6. The heat pipe 16 includes a condensation unit 24,an evaporation unit 26, and a piping 28. The condensation unit 24 isconnected to the cooling unit 22 of the refrigerator 14 in a manner thatheat exchange is enabled. By causing the condensation unit 24 and thecooling unit 22 to exchange heat, the refrigerant in the condensationunit 24 is cooled, condensed, and turned into a liquid. For example, arefrigerant gas such as R740 (argon), R50 (methane), R14(tetrafluoromethane), and R170 (ethane) can be used as the refrigerant.A refrigerant, which has a standard boiling temperature lower than theminimum value of the target temperature of the storage chamber 6 thatcan be set in the refrigerator 14, is selected. This can be understoodfrom the fact that the storage chamber 6 is cooled by the heat pipe 16and so cannot be at a temperature equal to or lower than the boilingtemperature of the refrigerant unless the ambient temperature is anextremely low temperature. The standard boiling temperature of arefrigerant is a boiling temperature at the atmospheric pressure (1atm=101325 Pa). A value determined from a documented value or a publiclyknown vapor-liquid equilibrium curve data can be employed as thestandard boiling temperature.

More specifically, the condensation unit 24 includes, as shown in FIG.3, a condensation fin 30 and a refrigerant passage 32 formed by thegrooves of the condensation fin 30. The condensation fin 30 is connectedto the cooling unit 22. The cold of the cooling unit 22 is transferredto the refrigerant flowing in the refrigerant passage 32 via thecondensation fin 30. The refrigerant in a gasified state is turned intoa liquid in the refrigerant passage 32.

One end of the piping 28 is connected to the condensation unit 24. Morespecifically, one end of the piping 28 is connected to the refrigerantpassage 32. Further, the other end of the piping 28 is connected to theevaporation unit 26. The refrigerant is circulated between thecondensation unit 24 and the evaporation unit 26 via the piping 28.

The evaporation unit 26 is connected to the storage chamber 6 in amanner that heat exchange is enabled. In this embodiment, theevaporation unit 26 extends along the wall surface of the inner box 2 btoward the heat insulator. The refrigerant turned into a liquid in thecondensation unit 24 flows into the evaporation unit 26 via the piping28. In the evaporation unit 26, the refrigerant absorbs the heat fromthe storage chamber 6 and is evaporated. Evaporation of the refrigerantcools the interior of the storage chamber 6. The refrigerant turned intoa gas in the evaporation unit 26 flows into the refrigerant passage 32of the condensation unit 24 via the piping 28. The refrigerant iscondensed again and turned into a liquid in the condensation unit 24.

The condensation unit 24 is provided vertically above the evaporationunit 26. Therefore, the refrigerant turned into a liquid in thecondensation unit 24 is gravitationally transferred to the evaporationunit 26. In other words, the heat pipe 16 according to the embodiment isa so-called thermosiphon that circulates the refrigerantgravitationally.

As shown in FIG. 1, the piping 28 according to the embodiment includes afar-side connecting pipe 28 a and a near-side connecting pipe 28 b. Oneend of the far-side connecting pipe 28 a and one end of the near-sideconnecting pipe 28 b are connected to the refrigerant passage 32.Further, the evaporation unit 26 has a pipe shape, and the other end ofthe far-side connecting pipe 28 a is connected to one end of theevaporation unit 26. The other end of the evaporation unit 26 isconnected to the other end of the near-side connecting pipe 28 b.

A portion of the refrigerant flows from the refrigerant passage 32 intothe evaporation unit 26 via the far-side connecting pipe 28 a. Therefrigerant mainly cools the far side of the inner box 2 b (rear side ofthe storage chamber 6) before it reaches the lower end of theevaporation unit 26. The refrigerant evaporated and turned into a gas inthis process returns to the refrigerant passage 32 via the far-sideconnecting pipe 28 a. In other words, the liquefied refrigerant and thegasified refrigerant flow in the opposite directions in the evaporationunit 26 and the far-side connecting pipe 28 a. In this process, theliquid refrigerant flows near the circumference of the piping, and thegas refrigerant flows near the center of the piping.

Further, another portion of the refrigerant flows from the refrigerantpassage 32 into the evaporation unit 26 via the near-side connectingpipe 28 b. The refrigerant mainly cools the near side of the inner box 2b (front side of the storage chamber 6) before it reaches the lower endof the evaporation unit 26. The refrigerant evaporated and turned into agas in this process returns to the refrigerant passage 32 via thenear-side connecting pipe 28 b. In other words, the liquefiedrefrigerant and the gasified refrigerant flow in the opposite directionsin the evaporation unit 26 and the near-side connecting pipe 28 b. Inthis process, the liquid refrigerant flows near the circumference of thepiping, and the gas refrigerant flows near the center of the piping.

In other words, a refrigerant circulation path of the first systemincluding the far-side connecting pipe 28 a and a refrigerantcirculation path of the second system including the near-side connectingpipe 28 b are formed between the refrigerant passage 32 and the lowerend of the evaporation unit 26.

Further, the heat pipe 16 according to the embodiment is structured tocirculate the refrigerant gravitationally so that the piping 28 isinclined with respect to the horizontal plane. Most of the liquidrefrigerant flowing in the pipe flows in the lower half of the pipe inthe vertical direction. For the purpose of circulating the refrigerantsmoothly, the larger than the angle of inclination of the pipe, thebetter. Meanwhile, a large angle of inclination of the pipe results in alarger height of the low-temperature storage 1. As a result, theworkability experienced when housing the object that should be stored inthe storage chamber 6 is lowered. For this reason, the angle ofinclination of the pipe is preferably about 10 degree.

The heat pipe 16 may be structured to circulate the refrigerant by acapillary force. In this case, the far-side connecting pipe 28 a isdefined as an outward path unit, and the near-side connecting pipe 28 bis defined as a return path unit. A circulation path of refrigerantconnecting the refrigerant passage 32, the outward path unit, theevaporation unit 26, and the return path unit in this sequence isformed.

The refrigerant chamber 18 is a storage tank connected to the heat pipe16 to pool the refrigerant of the heat pipe 16. The refrigerant chamber18 is connected to the refrigerant passage 32 of the condensation unit24 via a pipe 34. The refrigerant can go back and forth between the heatpipe 16 and the refrigerant chamber 18 via the pipe 34. When thepressure in the heat pipe 16 is increased, a portion of the refrigerantmoves from the heat pipe 16 to the refrigerant chamber 18. When thepressure in the heat pipe 16 is decreased, a portion of the refrigerantmoves from the refrigerant chamber 18 to the heat pipe 16. In this way,the pressure in the heat pipe 16 is adjusted. This internal pressure ofthe heat pipe 16 is set to be equal to or higher than the atmosphericpressure.

The heat pipe temperature sensor 42 detects the temperature of the heatpipe 16. The heat pipe temperature sensor 42 can substantially measurethe temperature of the refrigerant. In this embodiment, the heat pipetemperature sensor 42 is provided on the lateral surface of the piping28 and detects the temperature of the piping 28 (hereinafter, referredto as piping temperature as appropriate). The piping 28 is less affectedby the temperature in the storage chamber 6 than the evaporation unit26. Further, the piping 28 is less affected by the temperature of thecooling unit 22 than the condensation unit 24. Thus, the temperature ofthe refrigerant can be measured more accurately than otherwise bydetecting the temperature of the piping 28.

Preferably, the heat pipe temperature sensor 42 detects the temperaturein a portion of the piping 28 extending in the machine room 4. Morepreferably, the heat pipe temperature sensor 42 detects the temperatureat the center of the portion of the piping 28 extending in the machineroom 4. The center is a region including the middle point equallydistanced from the ends of the portion extending in the machine room 4.Temperature detection by the heat pipe temperature sensor 42 is easilyaffected by a localized inflow of heat. Meanwhile, the piping 28 extendsfrom the heat insulation box body 2 to the machine room 4. At theboundary of the machine room 4 with the heat insulation box body 2,localized inflow of heat by way of the boundary could occur. Therefore,the end of the portion of the piping 28 extending in the machine room 4toward the heat insulation box body 2 is easily affected by thelocalized inflow of heat. Thus, the temperature of the refrigerant canbe measured more accurately than otherwise by causing the heat pipetemperature sensor 42 to detect the temperature at the center of theportion of the piping 28 extending in the machine room 4. Further, it ispreferred that the heat pipe temperature sensor 42 be provided in aregion on the lateral surface of the piping 28 that faces downward inthe vertical direction. This is because the liquefied refrigerant flowson the lower side of the piping 28 in the vertical direction.

The heat pipe temperature sensor 42 and the inside temperature sensor 44are sensors such as a thermoelectric couple and a resistance temperaturedetector in which the electrical characteristics vary depending on thetemperature. A thermoelectric couple outputs a thermal electromotiveforce, which is commensurate with a temperature difference between thetemperature at a reference junction and the temperature at a temperaturemeasuring junction, to the temperature measuring junction in the form ofa voltage. The temperature value corresponding to the voltage value isidentified. The resistance temperature detector is exemplified by aplatinum thin film resistance temperature detector. The platinum thinfilm resistance temperature detector is exemplified by PT100, which hasa resistance value of 100Ω at 0° C., PT1000, which has a resistancevalue of 1000 Ω at 0° C., etc. These detectors are defined domesticallyin JISC1604. These resistance temperature detectors measure theresistance value that varies depending on the temperature of thetemperature measuring junction. The resistance temperature detectorsconvert the resistance value into a temperature value in accordance witha predetermined conversion formula or a conversion table and outputs thetemperature value. The temperature sensors output the temperature valueto the control unit 36. The temperature information transmitted to thecontrol unit 36 may not be a direct temperature value but may be avoltage value, a current value, a resistance value, etc. commensuratewith the the temperature value. Hereinafter, these will be genericallyreferred to as detection values. In performing control, however, itshould be considered that the variation in the voltage value, etc. withrespect to the temperature value may not be linear depending on the typeof sensor used. A publicly known sensor may be used as the heat pipetemperature sensor 42 and the inside temperature sensor 44. The heatpipe temperature sensor 42 and the inside temperature sensor 44 may notbe of the same type so long as the detection value is ultimately outputon the same scale.

The control unit 36 controls the driving of the refrigerator 14 based onthe result of detection by the heat pipe temperature sensor 42. Thecontrol unit 36 controls the refrigerator 14 so that the temperature ofthe heat pipe 16 does not fall below the standard boiling temperature ofthe refrigerant. The control unit 36 is implemented in hardware such asa device or a circuit exemplified by an amplifier, a digital signalprocessor, a CPU and a memory of a computer, etc. The control unit 36 isalso implemented by a loop control circuit or control software such as acomputer program. It will be understood by those skilled in the art thatthe control unit 36 may be implemented in a variety of manners by acombination of hardware and software.

A description will now be given of control performed by the control unit36 according to the embodiment. FIG. 4 is a flowchart showing an exampleof control performed in the refrigeration device according toembodiment 1. The refrigeration device 12 is operated as the controlunit 36 performs the flow repeatedly according to a predetermined timingschedule.

The control unit 36 according to the embodiment generates a signal forcontrolling the driving of the refrigerator 14 based on the result ofdetection by the inside temperature sensor 44 in addition to the resultof detection by the heat pipe temperature sensor 42. More specifically,the temperature of the piping and the inside temperature are firstdetected by the heat pipe temperature sensor 42 and the insidetemperature sensor 44, as shown in FIG. 4 (S101). The control unit 36acquires the detection value commensurate with the pipe temperature fromthe heat pipe temperature sensor 42 and acquires the detection valuecommensurate with the inside temperature from the inside temperaturesensor 44. A determination is then made as to whether the differencebetween the piping temperature and the standard boiling temperature ofthe refrigerant exceeds a predetermined value (S102). This makes itpossible to determine whether the temperature of the piping 28 fallsbelow the standard boiling temperature of the refrigerant, i.e., whetherthe temperature of the refrigerant falls below the standard boilingtemperature. The predetermined value can be set as appropriate based onan experiment by the designer or simulation.

When the difference between the piping temperature and the standardboiling temperature of the refrigerant exceeds the predetermined value(Y in S102), a control signal for controlling the refrigerator 14 basedon the inside temperature is generated (S103). Specifically, the controlunit 36 adjusts the output of the refrigerator 14 based on the result ofdetection by the inside temperature sensor 44 and, specifically, thesignal based on the detection value acquired from the inside temperaturesensor 44, so that the inside temperature is within a predeterminedrange with respect to a predetermined target temperature. For example,the control unit 36 detects a difference between the target temperatureand the current inside temperature and adjusts the output of therefrigerator 14 based on the difference. The target temperature is setby, for example, the user of the low-temperature storage 1. Thepredetermined range can be set as appropriate based on an experiment bythe designer or simulation.

An ordinary, publicly known method of adjustment can be used to adjustthe output of the refrigerator 14. Such output adjustment is exemplifiedby simple on/off control whereby the output is stopped when thedifference between the target temperature and the current insidetemperature resides within a predetermined range, and the output isresumed when the difference exceeds the predetermined range. In the casean inverter circuit etc. is provided as an output adjustment circuit andthe output of the refrigerator 14 can be changed continuously, theoutput value may be adjusted continuously by so-called PID control. Thisenables more stable temperature control.

When the difference between the piping temperature and the standardboiling temperature of the refrigerant is equal to or smaller than thepredetermined value (N in S102), a restricted control signal for therefrigerator 14 is generated (S104). In other words, the output of therefrigerator 14 is restricted irrespective of the result of detection bythe inside temperature sensor 44. The control unit 36 generates a signalfor controlling the refrigerator 14 based on the detection valueacquired from the heat pipe temperature sensor 42, so that the pipingtemperature does not fall below the standard boiling temperature of therefrigerant. This control is performed in preference to control of theinside temperature. The predetermined value can be set as appropriatebased on an experiment by the designer or simulation.

For example, the control unit 36 stores the standard boiling temperatureof the refrigerant filling the heat pipe 16. The control unit 36restricts the refrigerator 14 when the difference between the currentdetection value of the heat pipe temperature sensor 42 and the detectionvalue (the value is stored in the control unit 36 in advance) output bythe heat pipe temperature sensor 42 when the piping temperature is thestandard boiling temperature of the refrigerant is equal to or smallerthan the predetermined value. By way of one example, the control unit 36stops driving the refrigerator 14 when the difference between the pipingtemperature and the standard boiling temperature of the refrigerator isequal to or smaller than the predetermined value. By way of anotherexample, in the case an inverter circuit, etc. is provided as an outputadjustment circuit and the output of the refrigerator 14 can be changedcontinuously, the output of the refrigerator 14 may be restricted sothat the piping temperature does not fall below the standard boilingtemperature of the refrigerator, while the refrigerator 14 is drivencontinuously.

The control signal for controlling the refrigerator 14 generated in stepS103 or step S104 is output to the refrigerator 14, and the refrigerator14 is driven with the output value as set (S105). When, as a result ofrestricting the output of the refrigerator 14 in this route, the pipingtemperature is increased, and the difference between the pipingtemperature and the standard boiling temperature of the refrigerantexceeds the predetermined value in the subsequent routines (Y in S102),control of the refrigerator 14 based on the result of detection by theinside temperature sensor 44 is resumed (S103).

As described above, the refrigeration device 12 according to theembodiment is provided with the refrigerator 14, the heat pipe 16, theheat pipe temperature sensor 42, and the control unit 36. The heat pipetemperature sensor 42 detects the temperature of the heat pipe 16. Thecontrol unit 36 controls the driving of the refrigerator 14 based on theresult of detection by the heat pipe temperature sensor 42 so that thetemperature of the heat pipe 16 does not fall below the standard boilingtemperature of the refrigerant, i.e., is equal to or higher than thestandard boiling temperature. When the temperature of the heat pipe 16falls below the standard boiling temperature of the refrigerant,liquification of the refrigerant advances to shift the vapor-liquidequilibrium state, with the result that the internal pressure of theheat pipe 16 might be less than the atmospheric pressure. This isaddressed by controlling the driving of the refrigerator 14 so that thetemperature of the heat pipe 16 is equal to or higher than the standardboiling temperature of the refrigerant, thereby preventing the internalpressure of the heat pipe 16 from becoming less than the atmosphericpressure. In other words, it is guaranteed that the refrigerant in theheat pipe 16 is in the vapor-liquid equilibrium at a pressure equal toor higher than the atmospheric pressure, provided that the temperatureof the heat pipe 16 is equal to or higher than the standard boilingtemperature of the refrigerator. As a result, entry of ambient air intothe heat pipe 16 is inhibited.

When it is possible to inhibit entry of ambient air into the heat pipe16, the internal pressure of the heat pipe 16 is prevented from beingincreased excessively even if the refrigerator 14 is stopped and thetemperature of the refrigerant is increased. Accordingly, the heat pipe16 is prevented from being damaged or broken. Also, corrosion of theheat pipe 16 due to entry of ambient air is avoided. It is conceivableto monitor the internal pressure of the heat pipe 16 by a pressuresensor to prevent damage to the heat pipe 16. However, the cost ofemploying the heat pipe temperature sensor 42 is lower than the cost ofemploying a pressure sensor.

The heat pipe temperature sensor 42 according to the embodiment detectsthe temperature of the piping 28 of the heat pipe 16 that connects thecondensation unit 24 and the evaporation unit 26. This makes it possibleto understand the temperature of the refrigerant in the vapor-liquidequilibrium state (vapor-liquid equilibrium temperature) moreaccurately. By detecting the temperature of the portion of the piping 28extending in the machine room 4 and, more particularly, the temperatureat the center of the portion, the vapor-liquid equilibrium temperatureis known more accurately. Accordingly, the internal pressure of the heatpipe 16 is prevented from becoming less than atmospheric pressure moreproperly, by controlling the driving of the refrigerator 14 so that thetemperature at the portion does not fall below the standard boilingtemperature of the refrigerant.

The relationship between the temperature and the internal pressure ofthe heat pipe 16, internal pressure adjustment of the heat pipe 16performed by controlling the driving of the refrigerator 14, and therelationship between the designed inside temperature and the standardboiling temperature of the refrigerant described above are discoveredthrough our study.

Embodiment 2

The refrigeration device according to embodiment 2 differs significantlyfrom the refrigeration device according to embodiment 1 in respect ofthe detail of control by the control unit 36. A description of therefrigeration device according to embodiment 2 will be given below,highlighting the feature different from that of embodiment 1. Commonfeatures are described briefly, or a description thereof is omitted.

As in embodiment 1, the refrigeration device 12 according to embodiment2 includes the refrigerator 14, the heat pipe 16, the heat pipetemperature sensor 42, the inside temperature sensor 44, and the controlunit 36. The control unit 36 controls the refrigerator 14 so that thetemperature of the heat pipe 16 does not fall below the standard boilingtemperature of the refrigerant.

Further, the control unit 36 according to this embodiment controls thedriving of the refrigerator 14 based on the result of detection by theheat pipe temperature sensor 42 and the inside temperature sensor 44, asshown in FIG. 5. FIG. 5 is a flowchart showing an example of controlperformed by the refrigeration device according to embodiment 2. Theflow is is performed by the control unit 36 repeatedly according to apredetermined timing schedule.

As shown in FIG. 5, the inside temperature and the piping temperatureare detected first (S201). The control unit 36 acquires the detectionvalue commensurate with the inside temperature from the insidetemperature sensor 44 and acquires the detection value commensurate withthe piping temperature from the heat pipe temperature sensor 42.Subsequently, the control unit 36 generates a first control value Abased on the inside temperature and a second control value B based onthe piping temperature (S202).

The control unit 36 generates the first control value A based on thedifference between the inside temperature detected by the insidetemperature sensor 44 and the target temperature of the storage chamber6 and generates the second control value B based on the differencebetween the piping temperature detected by the heat pipe temperaturesensor 42 and the standard boiling temperature of the refrigerant. Byway of one example, the first control value A based on the insidetemperature is generated from a difference between the detection value(the value is stored in the control unit 36 in advance) output by theinside temperature sensor 44 when the inside temperature is theuser-defined target temperature and the detection value detected by theinside temperature sensor 44 and corresponding to the current insidetemperature. The second control value B based on the piping temperatureis generated from a difference between the detection value output by theheat pipe temperature sensor 42 when the piping temperature is thestandard boiling temperature of the refrigerant and the detection valuedetected by the heat pipe temperature sensor 42 and corresponding to thecurrent piping temperature. Inside temperature control performed sincethe detection of the inside temperature until the generation of thefirst control value A and piping temperature control performed since thedetection of the piping temperature until the calculation of the secondcontrol value B are, for example, PID control and are performed inparallel with each other. In inside temperature control, the firstcontrol value A is set so that the inside temperature is accommodated ina predetermined range with respect to the target temperature. Thepredetermined range can be set as appropriate based on an experiment bythe designer or simulation. In piping temperature control, the secondcontrol value B is set so that the piping temperature is not lower thanthe standard boiling temperature of the refrigerant. As described inembodiment 1, the refrigerant should be selected so that the standardboiling temperature of the refrigerant is lower than the preset value ofthe inside temperature.

A determination is then made as to whether the first control value A issmaller than the second control value B (S203). When the first controlvalue A is smaller than the second control value B (Y in S203), thedriving voltage based on the first control value A is applied to therefrigerator 14 (S204). When the first control value A is equal orlarger than the second control value B (N in S203), the driving voltagebased on the second control value B is applied to the refrigerator 14(S205). As a result, the refrigerator 14 is driven by the drivingvoltage generated based on the smaller of the first control value A andthe second control value B (S206).

According to this control, the driving voltage based on one (thesmaller) of the control values generated based on the inside temperaturecontrol and piping temperature control is applied to the refrigerator14. In other words, application of the voltage to the refrigerator 14 iscontinuous. In this way, abrupt change in power supply to therefrigerator 14 is avoided.

FIGS. 6A and 6B are charts showing an example of transition of theinside temperature and the piping temperature. As shown in FIG. 6A, thefirst control value A could be always smaller than the second controlvalue B when the preset value of the inside temperature (i.e., thetarget temperature of the storage chamber 6) is relatively high and isremote from the standard boiling temperature of the refrigerant. Ininside temperature control, the inside temperature is controlled so thatthe inside temperature reaches the preset value promptly. In otherwords, the integration gain in PID control is high. For this reason, atemporary overshoot of the inside temperature could occur. Further, thetemperature difference between the inside temperature and the pipingtemperature is large while the inside temperature keeps dropping. Theinside temperature surpasses the preset value and then approaches thepreset value gradually until it is stabilized ultimately, and the firstcontrol value A grows smaller in that process. For this reason, thetemperature difference between the inside temperature and the pipingtemperature will be decreased.

When, as shown in FIG. 6B, the preset value of the indoor temperatureand the standard boiling temperature are close to each other, on theother hand, the second control value B could be smaller than the firstcontrol value A temporarily while the indoor temperature is dropping. Inpiping temperature control, it is necessary to control the pipingtemperature not to fall below the standard boiling temperature. For thisreason, it is necessary to configure the integration gain in PID controlto be low. Therefore, the integration gain in piping temperature controlis lower than the integration gain in inside temperature control. Forthis reason, an overshoot of the inside temperature could be avoided.Further, the first control value A is smaller than the second controlvalue B, and the temperature difference between the inside temperatureand the piping temperature is large while the inside temperature keepsdropping. When the inside temperature approaches the preset value, thesecond control value B becomes smaller than the first control value A ata certain point of time. The control value input to the refrigerator 14will be the second control value B smaller that the first control valueA so that the temperature difference between the inside temperature andthe piping temperature will be decreased. In this process, the insidetemperature is lowered to approach the piping temperature. When theinside temperature further approaches the preset value subsequently, thefirst control value A drops gradually until the first control value Abecomes smaller than the second control value B at a certain point oftime. The temperature difference between the inside temperature and thepiping temperature will be decreased further. In this process, thepiping temperature is increased to approach the inside temperature.

As described above, the internal pressure of the heat pipe 16 isprevented from being less than the atmospheric pressure according alsoto the refrigeration device 12 of this embodiment. As a result, entry ofambient air into the heat pipe 16 is inhibited.

Embodiment 3

The refrigeration device according to embodiment 3 differs significantlyfrom the refrigeration device according to embodiments 1, 2 in that itincludes a plurality of combinations each including the refrigerator 14,the heat pipe 16, and the heat pipe temperature sensor 42. The featuresof the refrigeration device according to embodiment 3 that are differentfrom the features of embodiments 1, 2 will be described mainly. Commonfeatures will be described briefly, or a description thereof will beomitted.

FIG. 7A is a perspective view showing a schematic structure of alow-temperature storage in which the refrigeration device according toembodiment 3 is installed. FIG. 7B is a plan view showing a schematicstructure of the low-temperature storage. The refrigeration device 12according to this embodiment installed in the low-temperature storage 1(1B) includes a plurality of combinations each including therefrigerator 14, the heat pipe 16 and the heat pipe temperature sensor42. By way of one example, a description will be given of therefrigeration device 12 including a first refrigeration unit 12A as thefirst combination and a second refrigeration unit 12B as the secondcombination. The number of combinations is not limited to two.

The features of the refrigerator 14, the heat pipe 16, and the heat pipetemperature sensor 42 provided in each of the first refrigeration unit12A and the second refrigeration unit 12B are identical those of therefrigeration device 12 according to embodiment 1. The refrigerantcircuits of the respective refrigeration units are independent from eachother. Further, the refrigeration device 12 is provided with the controlunit 36 common to the first refrigeration unit 12A and the secondrefrigeration unit 123. In other words, one control unit 36 controls therefrigerators 14 of the respective refrigeration units. The control unit36 receives a signal from each of the heat pipe temperature sensor 42 ofthe first refrigeration unit 12A and the heat pipe temperature sensor 42of the second refrigeration unit 12B.

The control unit 36 controls the refrigerators 14 of the firstrefrigeration unit 12A and the second refrigeration unit 12B based onthe common piping temperature. The control unit 36 according to theembodiment controls the driving of the refrigerators 14 based on thelowest of the temperatures detected by the heat pipe temperature sensors42 of the first refrigeration unit 12A and the second refrigeration unit12B. FIG. 8 is a flowchart showing an example of control performed bythe refrigeration device according to embodiment 3. The flow is isperformed by the control unit 36 repeatedly according to a predeterminedtiming schedule.

As shown in FIG. 8, the inside temperature, the piping temperature ofthe first refrigeration unit 12A, and the piping temperature of thesecond refrigeration unit 12B are first detected (S301). The controlunit 36 acquires the detection value of the inside temperature from theinside temperature sensor 44 (see FIG. 2). The control unit 36 alsoacquires the respective detection values of the piping temperature fromthe heat pipe temperature sensors 42 of the respective refrigerationunits. Subsequently, the first control value A based on the insidetemperature, the second control value B1 based on the piping temperatureof the first refrigeration unit 12A, and the second control value B2based on the piping temperature of the second refrigeration unit 12B aregenerated (S302). The method of generating the first control value A isthe same as the method of generating the first control value A inembodiment 2. The method of generating the second control value B1 andthe second control value B2 is the same as the method of generating thesecond control value B in embodiment 2.

A determination is then made as to whether the second control value B1is smaller than the second control value B2 (S303). When the secondcontrol value B1 is smaller than the second control value B2 (Y inS303), the second control value B1 is determined to be a representativecontrol value C based on the piping temperature (S304). When the secondcontrol value B1 is equal to or larger than the second control value B2(N in S303), the second control value B2 is determined to be therepresentative control value C based on the piping temperature (S305).

A determination is then made as to whether the first control value A issmaller than the representative control value C (S306). When the firstcontrol value A is smaller than the representative control value C (Y inS306), the driving voltage based on the first control value A is appliedto the refrigerators 14 of the respective refrigeration units (S307).When the first control value A is equal to or larger than therepresentative control value C (N in S306), the driving voltage based onthe representative control value C is applied to the refrigerators 14 ofthe respective refrigeration units (S308). The refrigerators 14 of therespective refrigeration units are driven accordingly (S309).

According to the control, the smaller of the second control value B1calculated based on the piping temperature of the first refrigerationunit 12A and the second control value B2 calculated based on the pipingtemperature of the second refrigeration unit 12B is compared with thefirst control value A calculated based on the inside temperature. Thismakes it possible to make the output balance in the respectiverefrigeration units constant, maintaining the internal pressure of theheat pipes 16 of the respective refrigeration units to be equal to orhigher than the atmospheric pressure. As a result, the temperaturedistribution in the storage can be maintained uniform. Further, theinternal pressure of the heat pipes 16 in the respective refrigerationunits can be maintained to be equal to or higher than the atmosphericpressure more properly.

The driving of the refrigerators 14 in the first refrigeration unit 12Aand the second refrigeration unit 12B may be controlled independently.In this case, the second control value B1 is calculated in the firstrefrigeration unit 12A based on the piping temperature. Further, thesecond control value B2 is calculated in the second refrigeration unit12B based on the piping temperature. Further, the first control value Ais calculated based on the inside temperature. The first control value Ais common to the respective refrigeration units. In the firstrefrigeration unit 12A, the magnitude of the first control value A andthat of the second control value B1 are compared and the driving voltagebased on the smaller of the control values is applied to therefrigerator 14. Further, in the second refrigeration unit 12B, themagnitude of the first control value A and that of the second controlvalue B2 are compared and the driving voltage based on the smaller ofthe control values is applied to the refrigerator 14.

The embodiments of the present disclosure are not limited to thosedescribed above and the embodiments may be combined, or various furthermodifications such as design changes may be made based on the knowledgeof a skilled person. The embodiments resulting from such combinations orfurther modification are also within the scope of the presentdisclosure. New embodiments created by combining embodiments ormodifying the embodiment will provide the combined advantages of theembodiment and the variation.

Optional combinations of the aforementioned constituting elements, andimplementations of the invention in the form of methods, apparatuses,and systems may also be practiced as additional modes of the presentinvention.

What is claimed is:
 1. A refrigeration device comprising: arefrigerator; a heat pipe that includes a condensation unit connected tothe refrigerator in a manner that heat exchange is enabled and adaptedto condense a refrigerant, includes an evaporation unit connected to astorage chamber for housing an object that should be stored in a mannerthat heat exchange is enabled and adapted to evaporate the refrigerant,and includes a piping for circulating the refrigerant between thecondensation unit and the evaporation unit; a heat pipe temperaturesensor that detects a temperature of the heat pipe; and a control unitthat controls driving of the refrigerator based on a result of detectionby the heat pipe temperature sensor, wherein the control unit controlsthe refrigerator so that the temperature of the heat pipe does not fallbelow a standard boiling temperature of the refrigerant.
 2. Therefrigeration device according to claim 1, further comprising: an insidetemperature sensor that detects a temperature of the storage chamber,wherein the control unit controls the driving of the refrigerator basedon a result of detection by the heat pipe temperature sensor and theinside temperature sensor, and the control unit controls therefrigerator based on the result of detection by the inside temperatureso that the temperature of the storage chamber is within a predeterminedrange with respect to a predetermined target temperature, when adifference between the temperature of the heat pipe and the standardboiling temperature of the refrigerant is equal to or smaller than apredetermined value, the control unit restricts an output of therefrigerator irrespective of the result of detection by the insidetemperature sensor, and when the difference between the temperature ofthe heat pipe and the standard boiling temperature of the refrigerantexceeds the predetermined value, the control unit resumes controllingthe refrigerator based on the result of detection by the insidetemperature sensor.
 3. The refrigeration device according to claim 2,wherein when the difference between the temperature of the heat pipe andthe standard boiling temperature of the refrigerant is equal to orsmaller than the predetermined value, the control unit stops driving therefrigerator.
 4. The refrigeration device according to claim 1, furthercomprising: an inside temperature sensor that detects a temperature ofthe storage chamber, wherein the control unit controls the driving ofthe refrigerator based on a result of detection by the heat pipetemperature sensor and the inside temperature sensor, and the controlunit generates a first control value based on a difference between thetemperature of the storage chamber detected by the inside temperaturesensor and a target temperature of the storage chamber, the control unitgenerates a second control value based on a difference between thetemperature of the heat pipe detected by the heat pipe temperaturesensor and the standard boiling temperature of the refrigerant, and thecontrol unit controls the refrigerator based on the smaller of the firstcontrol value and the second control value.
 5. The refrigeration deviceaccording to claim 1, wherein the heat pipe temperature sensor detects atemperature of the piping.
 6. The refrigeration device according toclaim 5, wherein the refrigerator is provided in a machine room providedat a distance from the storage chamber, a portion of the piping isprovided in the machine room, and the heat pipe temperature sensordetects a temperature of the portion in the piping.
 7. The refrigerationdevice according to claim 1, the refrigeration device includes aplurality of combinations each including the refrigerator, the heatpipe, and the heat pipe temperature sensor, and the control unitcontrols the driving of the refrigerators based on the lowest of thetemperatures detected by the heat pipe temperature sensors or based onthe temperature in the storage chamber.
 8. The refrigeration deviceaccording to claim 1, wherein the refrigerant has a standard boilingtemperature lower than the lowest of a target temperature of the storagechamber that can be set in the refrigerator.